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package javax.xml.bind;

import javax.xml.namespace.QName;
import java.io.Serializable;

/**
 * <p>JAXB representation of an Xml Element.</p>
 *
 * <p>This class represents information about an Xml Element from both the element declaration
 * within a schema and the element instance value within an xml document with the following
 * properties <ul> <li>element's xml tag <b><tt>name</tt></b></li> <li><b><tt>value</tt></b>
 * represents the element instance's atttribute(s) and content model</li> <li>element declaration's
 * <b><tt>declaredType</tt></b> (<tt>xs:element @type</tt> attribute)</li> <li><b><tt>scope</tt></b>
 * of element declaration</li> <li>boolean <b><tt>nil</tt></b> property. (element instance's
 * <tt><b>xsi:nil</b></tt> attribute)</li> </ul>
 *
 * <p>The <tt>declaredType</tt> and <tt>scope</tt> property are the JAXB class binding for the xml
 * type definition. </p>
 *
 * <p><b><tt>Scope</tt></b> is either {@link GlobalScope} or the Java class representing the complex
 * type definition containing the schema element declaration. </p>
 *
 * <p>There is a property constraint that if <b><tt>value</tt></b> is <tt>null</tt>, then
 * <tt>nil</tt> must be <tt>true</tt>. The converse is not true to enable representing a nil element
 * with attribute(s). If <tt>nil</tt> is true, it is possible that <tt>value</tt> is non-null so it
 * can hold the value of the attributes associated with a nil element. </p>
 *
 * @author Kohsuke Kawaguchi, Joe Fialli
 * @since JAXB 2.0
 */

public class JAXBElement<T> implements Serializable {

  /**
   * xml element tag name
   */
  final protected QName name;

  /**
   * Java datatype binding for xml element declaration's type.
   */
  final protected Class<T> declaredType;

  /**
   * Scope of xml element declaration representing this xml element instance.
   * Can be one of the following values:
   * - {@link GlobalScope} for global xml element declaration.
   * - local element declaration has a scope set to the Java class
   * representation of complex type defintion containing
   * xml element declaration.
   */
  final protected Class scope;

  /**
   * xml element value.
   * Represents content model and attributes of an xml element instance.
   */
  protected T value;

  /**
   * true iff the xml element instance has xsi:nil="true".
   */
  protected boolean nil = false;

  /**
   * Designates global scope for an xml element.
   */
  public static final class GlobalScope {

  }

  /**
   * <p>Construct an xml element instance.</p>
   *
   * @param name Java binding of xml element tag name
   * @param declaredType Java binding of xml element declaration's type
   * @param scope Java binding of scope of xml element declaration. Passing null is the same as
   * passing <tt>GlobalScope.class</tt>
   * @param value Java instance representing xml element's value.
   * @see #getScope()
   * @see #isTypeSubstituted()
   */
  public JAXBElement(QName name,
      Class<T> declaredType,
      Class scope,
      T value) {
    if (declaredType == null || name == null) {
      throw new IllegalArgumentException();
    }
    this.declaredType = declaredType;
    if (scope == null) {
      scope = GlobalScope.class;
    }
    this.scope = scope;
    this.name = name;
    setValue(value);
  }

  /**
   * Construct an xml element instance.
   *
   * This is just a convenience method for <tt>new JAXBElement(name,declaredType,GlobalScope.class,value)</tt>
   */
  public JAXBElement(QName name, Class<T> declaredType, T value) {
    this(name, declaredType, GlobalScope.class, value);
  }

  /**
   * Returns the Java binding of the xml element declaration's type attribute.
   */
  public Class<T> getDeclaredType() {
    return declaredType;
  }

  /**
   * Returns the xml element tag name.
   */
  public QName getName() {
    return name;
  }

  /**
   * <p>Set the content model and attributes of this xml element.</p>
   *
   * <p>When this property is set to <tt>null</tt>, <tt>isNil()</tt> must by <tt>true</tt>.
   * Details of constraint are described at {@link #isNil()}.</p>
   *
   * @see #isTypeSubstituted()
   */
  public void setValue(T t) {
    this.value = t;
  }

  /**
   * <p>Return the content model and attribute values for this element.</p>
   *
   * <p>See {@link #isNil()} for a description of a property constraint when
   * this value is <tt>null</tt></p>
   */
  public T getValue() {
    return value;
  }

  /**
   * Returns scope of xml element declaration.
   *
   * @return <tt>GlobalScope.class</tt> if this element is of global scope.
   * @see #isGlobalScope()
   */
  public Class getScope() {
    return scope;
  }

  /**
   * <p>Returns <tt>true</tt> iff this element instance content model
   * is nil.</p>
   *
   * <p>This property always returns <tt>true</tt> when {@link #getValue()} is null.
   * Note that the converse is not true, when this property is <tt>true</tt>,
   * {@link #getValue()} can contain a non-null value for attribute(s). It is
   * valid for a nil xml element to have attribute(s).</p>
   */
  public boolean isNil() {
    return (value == null) || nil;
  }

  /**
   * <p>Set whether this element has nil content.</p>
   *
   * @see #isNil()
   */
  public void setNil(boolean value) {
    this.nil = value;
  }

    /* Convenience methods
     * (Not necessary but they do unambiguously conceptualize
     *  the rationale behind this class' fields.)
     */

  /**
   * Returns true iff this xml element declaration is global.
   */
  public boolean isGlobalScope() {
    return this.scope == GlobalScope.class;
  }

  /**
   * Returns true iff this xml element instance's value has a different
   * type than xml element declaration's declared type.
   */
  public boolean isTypeSubstituted() {
    if (value == null) {
      return false;
    }
    return value.getClass() != declaredType;
  }

  private static final long serialVersionUID = 1L;
}
